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At present, the lifetime of engine oil is judged by chemically measuring the changes in its properties while running of an actual vehicle or by setting the standards for its replacement cycle in terms of travel distance and time. The advantage of the former is that the lifetime can be judged with a high degree of reliability, but its disadvantage is that information on the lifetime is difficult for users to obtain. The problem with the latter is that the standards are unreliable. Therefore, users need a simple and reliable method to evaluate the degradation of engine oil so they can determine the appropriate time to change it. We examined the possibility of evaluating the lifetime of engine oil by measuring its capacitance using a comb-shaped electrode. As a result, we found that the capacitance of four types of engine oil collected at markets tended to decrease during the initial stage of degradation and then increased in the later stage.

Diamond-Like Carbon (DLC) is a promising engine material for reducing friction and wear on sliding parts. By contrast, MoDTC lubricant additives are known to promote the wear of a-C:H films. However, the mechanism that promotes wear and the formation of tribofilms on DLC parts when in contact with molybdenum-based lubricant additives has not been sufficiently studied. The purpose of this research is to determine the wear promotion mechanism and formation of tribofilm on DLC by lubricant additives by comparing friction and wear properties. We conducted friction and wear tests using a tribometer with DLC (ta-C, ta-C:H, a-C, and a-C:H) blocks, FC250 (cast iron) rings, and oils containing lubricant additives (MoDTC, MoDTP, and Mo without DTC ligand) by observing and analyzing the sliding surfaces of specimens. No wear was observed for any of the DLCs (ta-C, ta-C:H, a-C:H, and a-C) in combination with oils containing MoDTP or Mo without DTC ligands.

To evaluate the influence of FAME, which has poor oxidation stability, on engine oil performance, an engine test was conducted under large volumes of fuel dilution by post-injection. The test showed that detergent consumption and polymerization of FAME were accelerated in engine oil, causing a severe deterioration in piston cleanliness and sludge protection performance of engine oil.

The use of Automatic Transmission Fluids (ATFs) with lower viscosity and excellent anti-shudder durability for wet clutch system will be effective for improving fuel saving performance in automatic transmissions. In this study, two ATF formulation techniques were examined. The first trial formulation is to improve fatigue life in gear components even if a lower viscosity ATF is used. The second one is to improve anti-shudder durability for wet lock-up clutch system in AT units. As to fatigue life performance, the relation between molecular weight of Viscosity Index Improver (VII) and film formation property in EHL contact regions were experimentally investigated. ATFs containing VIIs with lower molecular weight tend to increasing EHL film thickness, resulting in a longer gear pitting fatigue life. Calcium detergents and ashless friction modifiers in ATFs were found to give a great impact on the anti-shudder performance.

The deposition of ash derived from engine oil on the surface of diesel particle filters (DPF) has recently been reported to degrade the performance of the DPF. It is generally known that phosphorus in engine oil is adsorbed on the surface of an automotive exhaust catalyst, reducing the performance of the catalyst. Thus, the amounts of ash and phosphorus in engine oil have been decreased. We have developed a non-phosphorus, non-ash engine oil (NPNA) that does not contain metal-based detergents or zinc dialkyldithiophosphate (ZnDTP). Various engine tests were performed, and we confirmed that under normal running conditions, the NPNA oil had a sufficiently high piston detergency and wear resistance-two important requirements for engine oil-to meet current American and Japanese standards. However, the piston detergency of NPNA required further improvement when engine running conditions were more severe.

High viscosity index(HVI) petroleum base stock, with excellent temperature-viscosity characteristics, oxidation resistance, and low-evaporation properties, offers advantages as the base stock for high fuel economy engine oils, particularly because of its low-friction properties in the boundary and/or “E.H.L (Elastohydrodynamic Lubrication)” area due to its rheological characteristics. This research evaluated HVI base stock's low-friction properties. Upgrading the oil from 5W-30 to 5W-20 was also investigated. The friction properties of the HVI base stock were measured by a unit friction platform. The results show a 28% reduction in friction coefficient compared with the conventional, solvent refined oil, which is attributable to the high-pressure viscosity of the base oil.